IgA nephropathy and IgA vasculitis
- Lesion
The commonest glomerulonephritis in the world: abnormal IgA1 collects in the mesangium and causes recurrent bloody urine.
What it is
In IgA nephropathy, IgA1 molecules lacking galactose in their hinge region trigger autoantibodies; the resulting complexes lodge in the mesangium and activate complement through the alternative and lectin pathways. The same deposits plus a small-vessel vasculitis of skin, gut and joints define IgA vasculitis (Henoch-Schönlein purpura), mostly in children. Secondary IgA deposits occur in celiac disease and cirrhosis, where IgA clearance is reduced.
Structure
- Mesangial widening with more cells and matrix; some cases show segmental proliferation or sclerosis.
- Immunofluorescence shows dominant or codominant IgA in the mesangium.
- Electron microscopy shows electron-dense mesangial deposits.
- In IgA vasculitis the skin shows leukocytoclastic vasculitis with IgA in small vessels.
Step by step
- Genetic and mucosal factors increase production of galactose-deficient IgA1.
- The exposed hinge region is recognized by IgG or IgA autoantibodies.
- Immune complexes form in the blood and are poorly cleared.
- They lodge in the mesangium and activate complement via the alternative and lectin pathways.
- Mesangial cells proliferate and release cytokines; hematuria follows, with proteinuria in more active disease.
Hematuria after an infection: two diseases compared
| Feature | IgA nephropathy | Postinfectious GN |
|---|---|---|
| Timing after infection | One or two days | One to several weeks |
| Complement | Normal | Low C3 |
Clinical notes
- Painless episodes of brown urine in a young man after a cold; between episodes, microscopic hematuria persists.
- IgA vasculitis in a child: purpura, colicky pain (risk of intussusception), arthralgia and hematuria.
Test yourself
Think of the answer, then tap the question to see it.
What is abnormal about the IgA in IgA nephropathy?
IgA1 molecules lack galactose in the hinge region, which makes them antigenic and prone to forming complexes.
How does the timing of hematuria help separate IgA nephropathy from postinfectious GN?
IgA nephropathy follows the infection within a day or two; postinfectious GN appears after one to several weeks.
Which two diseases cause secondary mesangial IgA deposits?
Celiac disease and cirrhosis (reduced hepatic clearance of IgA).
Elsewhere in DurgiPedia
- Type III hypersensitivity (immune complexes)
- Mucosa-associated lymphoid tissue (tonsils, Peyer patches)
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: IgA nephropathy: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.